Obviously, Google and Apple censor Telegram channels and block them so that they can no longer be reached via the app if it has been downloaded via the Google Playstore or the Appstore. The canals can still be reached in other ways. So far there has been no official reason for bans - but of course you can imagine it. Telegram is known for rarely intervening in the channels, which is why it is also used by people who do not need a Ministry of Truth and have media skills.
If you would like to continue using Telegram on Android without censorship, you can find the app under the following link:
https://telegram.org/android
For iOS there is unfortunately no version that cannot be downloaded from the app store, unless you have a hacked version of the iPhone and can access the Telegram version yourself Go completing, downloading and installing.
Telegram is also available for the desktop under Windows / Mac / Linux and macOS
https://telegram.org/apps#desktop-apps
Or as a web client:
https://telegram.org/apps#web-apps